The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a safety valve with a flapper/flow tube friction reducer.
In a typical safety valve, a flow tube or opening prong is displaced relative to a flapper in order to open or close a production flow passage formed through the safety valve. In many instances, sand and other debris is produced through the flow passage, which causes dramatically increased friction in operation of the safety valve.
To counteract this increased friction, manufacturers of safety valves have generally attempted to increase the force used to displace the flow tube. Unfortunately, this solution has only limited effectiveness and applicability.
In the case of hydraulically operated safety valves, piston area is limited, increased pressure ratings for hydraulic conduits and pumps are expensive and sometimes unavailable, and available operating pressure differential is severely limited for deep set safety valves. Similar limitations are present for other types of safety valves (such as electrically, magnetically, etc. operated safety valves).
Even when sand and other debris is not being produced through a safety valve, damage can be caused when friction delays displacement of the flow tube during what is known as a “slam closure” of the safety valve. Increased friction due to sand and other debris makes this damage more likely.